This invention relates to the surgical art and has particular relationship to catheters for conducting electrical current to parts of the body. Specifically, catheters serve to conduct current to organs, such as the heart or the diaphragm, which are stimulated by electrical current. In the interest of relying here on concrete treatment of the invention to aid those skilled in the art to understand this invention, this application is on the whole confined to a catheter for a heart pacer. However, to the extent that this invention is applicable to parts of the body and organs other than the heart, such application is within the scope of this invention.
Typically, a catheter for a heart pacer includes a hollow closely-wound coil, typically of MP35N wire. MP35N is an alloy in weight percent of Ni35-Co35-Cr20-Mo10. The coil is encased in a jacket of silicone rubber. Where the heart is supplied from a pole of the supply through a single conductor with the opposite pole of the supply grounded, the cathether has at one end a plug which engages a socket or receptacle in the pacer. At the other end arcuate needles or like mechanisms for connection or suturing to the heart are provided. Where two conductors are used, like facilities are provided. The contraction of the heart muscle which the current from the catheter produces is dependent on the density of this current; i.e., on the magnitude of the current per unit area. The current density may be measured in amperes or milliamperes per square centimeter or square millimeter. The current density must exceed a predetermined threshold magnitude. Typically, the threshold current is 2 to 4 milliamperes per 10 square millimeter area at 5 volts and a 0.5 millisecond duration pulse. If threshold is too high, the muscle contraction does not take place. It is essential that the connection of the catheter to the heart be effective and reliable and of low resistance and be effected with a minimum of discomfort to the patient. It is also essential that the connection be such that the current density reliably exceeds the threshold current density. It is an object of this invention to provide a catheter which shall be capable of being so connected to the heart or other organ.
As a starting point of this invention, extensive work has been carried out with catheters having cooperative resiliently actuable hooks or jaws for connection to the heart muscle. Preliminary experiments had indicated that this catheter would operate satisfactorily. Such a catheter is shown in U.S. Pat. No. 4,011,875, Lehr, et al. A number of such catheters were implanted in dogs. It was found that these catheters operated erratically. A few operated satisfactorily over a relatively long time interval. The others supplied current of adequate density at the start, but the current fell off rapidly and in a relatively short time, a few days or a week, the necessary contraction of the heart muscle no longer took place.
It is an object of this invention to overcome the disadvantages of the above-described prior art and to provide a catheter for an implanted electrical generator which shall include resiliently actuable jaws for connection to the organ to be stimulated without major surgery such as open-heart surgery and without resulting discomfort or injury to the host and which shall reliably and for long time intervals conduct to the organ current of a density exceeding the required threshold current density.